The Moon’s Partially-Molten Layer: New Study Suggests a Goopy Zone Beneath the Surface

A recent study on the Moon’s changing shape and gravity is shedding light on the possibility of a partially-molten layer existing between its rocky mantle and solid metal core. Researchers from the NASA Goddard Space Flight Center and the University of Arizona have analyzed new data that indicates the Moon’s mass is unlikely to be solid all the way through, suggesting the presence of a thick, goopy zone that behaves like tides.

According to the researchers’ published paper, interior modeling suggests that the Moon’s rigidity can only be explained by the presence of a low-viscosity zone (LVZ) at the base of its mantle. This concept of a non-solid layer has been theorized by scientists for decades, but until now, conclusive evidence was lacking.

The study utilized data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) and Lunar Reconnaissance Orbiter to measure the lunar tidal changes caused by the gravitational pull of Earth and the Sun. By analyzing these readings, the researchers were able to estimate the yearly fluctuations in the Moon’s shape and gravitational field.

Computer models of the Moon’s interior suggest that a viscous layer beneath the solid mantle is necessary to explain the observed data, raising questions about the origin and heat source of this zone. The researchers propose that the mineral ilmenite, a titanium-iron oxide, may play a role in creating and maintaining the LVZ.

Comparisons are drawn between the Moon and Mars, where partial melt in ilmenite-rich layers has been inferred from seismic data. The presence of an LVZ at the lower base of the lunar mantle could have significant implications for the Moon’s thermal history and evolution.

While uncertainties remain about the Moon’s internal structure, ongoing research and potential seismic readings from a lunar base in the future could provide more insights into what lies beneath the surface. The study has been published in AGU Advances, offering a new perspective on the Moon’s composition and geological processes.